The present invention relates to a discharge lamp device including an arc tube mounted on the front surface of an insulating base and, in particular, to an insulating base for a discharge lamp device which supports an arc tube.
In FIG. 7 is shown a conventional discharge lamp device in which a pair of lead supports 2 and 3, which conduct energizing current to an arc tube, project forwardly of an insulating base 1 formed of synthetic resin. An arc tube 4 is supported by the supports 2 and 3. A globe 5 enclosing the arc tube 4 to screen ultraviolet rays is fixed to and held by the front surface of the base 1, so that ultraviolet rays generated by the arc tube 4 and which are in a wavelength range harmful to health are cut off by the globe 5. Reference numeral 6 designates a ceramic disk fixed to the front surface of the base 1 by suitable means such as a screw, an adhesive or the like, with the opening end portion of the globe 5 being bonded to the disk 6. Reference numerals 9a and 9b indicate a pair of terminals provided on and projecting from the rear surface side of the base 1. The terminals 9a and 9b are welded integrally to the lead supports 2 and 3, respectively, and the lead supports 2 and 3 are connected through metal support members a and b to leads 4a and 4b which are electrically connected to respective ones of the opposing electrodes of the arc tube 4.
However, in the above-mentioned conventional discharge lamp device, since the arc tube 4 is supported by the two lead supports 2 and 3, the resulting structure of the discharge lamp device is unavoidably complicated. Also, the globe 5 for screening of ultraviolet rays must be of a size sufficient to enclose the arc tube 4 and the two lead supports 2 and 3, which causes the discharge lamp device to be large in size.
To solve the above problems and to simplify the structure of the lamp device and thus realize a compact lamp device, there has been proposed a discharge lamp device, as disclosed in Japanese Patent Application No. Hei. 4-54709, in which the rear end portion of an arc tube 4 is engaged with and supported by a recessed portion 1a formed in the front surface of a base 1 to thereby reduce the number of lead supports used from two to one. In FIG. 8, reference numeral 7 designates a glass disk welded to the opening end of a globe 5, and 8, staking members used to fix the disk 7. Reference numeral 1b designates a lead support insertion hole, and 9a, a lead which is a terminal electrically connected to a lead support 2. The conductors of power supply cords L.sub.1 and L.sub.2 are connected to the terminals 9a and 9b, respectively. FIG. 9 is an enlarged perspective view of the base 1 of the discharge lamp device shown in FIG. 8, while FIG. 11 is a longitudinal sectional view of the base 1.
However, to mold a base 1 shown in FIG. 9, as shown by wide arrows in FIG. 10, molten resin is supplied into the cavity of a metal mold from six positions corresponding to the outer peripheral edge portions of the base; that is, the cavity of the metal mold for injection molding has a structure wherein gates serving as molten resin injection holes are positioned in the outer peripheral edge portion of the base to be molded. For this reason, in the outer peripheral edge portion of the conventional base 1, there are left gate traces, as indicated by P in FIG. 9, which makes the base 1 look less attractive. It is possible to remove the gate traces P by cutting or the like in a step subsequent to molding, but this, however, increases the number of steps and thus increases the cost of the base 1.
Also, the molten resin supplied into the cavity from the gates can flow smoothly into a large space area as shown by A in FIG. 10 because the flow resistance is small, but it is difficult for the molten resin to flow into a narrow space area indicated by B in FIG. 10 because the flow resistance is large. A weld can easily be generated in the latter case.
The arrows in FIG. 10 show the directions in which the molten resin supplied into the cavity from the gates flows; that is, the molten resin is first filled in the wide area indicated by A, and is finally filled in a separation wall (a narrow area indicated by B) interposed between the lead support insertion hole 1a and lead insertion hole 1b. Due to this, a weld W (see FIGS. 8 and 11) is generated in the separation wall between the two insertion holes 1a and 1b. The weld W degrades the insulation between the lead support 2 and lead 4b.